LOUISVILLE - Bob Leeper and Dan Seum, the Republican senators Democrats most love to hate, stymied efforts to have them tossed out of the General Assembly on Tuesday.

Mr. Seum won comfortably in a Jefferson County district against Democratic firefighter Bruce Roberts. Mr. Leeper also won in a much closer race against union organizer Larry Sanderson in the district surrounding Paducah, though Mr. Sanderson's camp said they planned to question some of the returns.

The math left the GOP with its Senate majority intact, with Republicans picking up a vacant seat in central Kentucky, making the margin 21-17, up from the current 20-18.

The outcome should end any question about the legitimacy of Republican control of the Senate, which took place only after Mr. Seum and Mr. Leeper changed their party affiliations in 1999.

"They can no longer say that this is a majority that we did not earn," said Senate President David Williams. "This was won at the ballot box."

Incumbents held sway across the board, with changes in party affiliation taking place in vacant seats.

Republican incumbent Sen. Julie Denton in Louisville easily held off a challenge from Franklin Jelsma, a Cabinet secretary in former Gov. Brereton Jones' administration.

Among Democrats, Sen. David Boswell in Owensboro held off Rep. Mark Treesh in a very close race.

Democratic Majority Leader David Karem of Louisville said he could not explain the lack of success. "We fielded what we thought were incredibly strong candidates," Mr. Karem said. "This is one that the experts will have to figure out and I'm not one of those."

There was some swapping of House seats, but Republicans had no hope of loosening the stranglehold Democrats have on the House, which was in their control 66-34 in the last two years.

A majority in the Senate, however slim it has been, proved decisive in several legislative battles.

First Mr. Seum, then Mr. Leeper changed parties in 1999 after a Democratic upheaval caused by Sen. Larry Saunders when he enlisted Republicans to overthrow the Democratic leadership in the Senate.

Mr. Seum, who had always been a maverick even among Democrats, managed to get virtually an entirely new district drawn for him to seek re-election. And the GOP poured money into his race.

Mr. Leeper, a Paducah chiropractor who had been elected the previous year with the help of Democratic funds, has tried for three years to calm some of the outrage at his defection. Democrats selected Larry Sanderson, a union organizer with a long reputation of working with corporate interests, to challenge him.